All those involved, and most of those following the bloodshed in Gaza from afar, are sure who is in the right and who is in the wrong. They know who the innocent victims are and who are the wicked perpetrators. These certainties are held equally firmly by those who will be demonstrating in solidarity with the Palestinians in London today and those who plan to stage similar shows of support for Israel later this month.

Both sides see the conflict in moral terms. For supporters of the Palestinians, it could not be clearer. Israel is committing a war crime, killing people in their hundreds, hammering a besieged population from the sky (and soon perhaps on the ground too), claiming to aim only at Hamas but inevitably striking those civilians who get in the way.

Israel's cheerleaders are just as clear. Israel is the victim, hitting out now only belatedly and in self-defence. Its southern citizens have sat terrorised in bomb shelters, fearing the random rockets of Hamas, since 2005, longer than any society could tolerate without fighting back.

Both sides say they would have maintained the six-month ceasefire that had held - albeit imperfectly - until December 19 had the other side not broken it first. And who did break the deal first, Hamas with its rockets or Israel with its blockade? Both sides point at the other with equal vehemence, a Newtonian chain of claimed action and reaction that can stretch back to infinity.

So perhaps a more useful exercise - especially for those who long for an eventual peace with both sides living side by side - is not to ask whether the current action is legitimate, but whether it is wise.

Israel, say its spokesmen, seeks not to trigger an Iraq-style "regime change" in Gaza but simply to alter Hamas' calculus, so it concludes that hurling rockets is against its own interests. Israel hopes thereby to reassert its long-cherished deterrence, so damaged in Lebanon in 2006. Hamas will be taught a lesson, abide by an enduring ceasefire and leave Israel's southern border quiet. Israel can then get on with pursuing a pact with the Fatah-led Palestinians of the West Bank.

That sounds coherent, but does it make sense? After this first phase of the conflict, Israeli officials say yes. They boast that Hamas' command and control systems have been shattered, and that its leaders are in hiding 4m under ground.

But there are immediate questions, eerily similar to the ones that surfaced in Lebanon two years ago. How exactly does this end? If Israeli tanks go into Gaza, won't they get bogged down in the mud and narrow streets of the refugee camps, terrain known intimately by Hamas?

And these are only the most obvious, current concerns. The grounds for questioning the wisdom of Operation Cast Lead, even from Israel's own point of view, go much deeper.

First, even if Israel gets the quiet it wants there is every reason to believe it could have got that without resorting to war. The longtime Palestinian analyst and negotiator Hussein Agha says it would have been "straightforward: if they had lifted the blockade, the rockets would have stopped".

Some diplomatic sources dispute this, arguing that Hamas actually saw an advantage in the sanctions regime: "opening up would have loosened Hamas' grip," says one. Hence the cases of Hamas firing on border crossings as they were opened. But most Palestinians insist that a relaxation of the blockade would have granted Hamas its key objective - a chance to prove it can govern effectively - and it would not have jeopardised that with rocket fire. It would have had too much to lose.

Put that to Israelis, and they admit that prospect was unpalatable too: they can't allow Hamas, a movement whose charter drips with antisemitism and calls for Israel's eradication, to gain the appearance of legitimacy. But if, as Israel insists, its chief objective is quiet in the south, then there was at least another, non-military path it could have taken - one that those who know Hamas best insist would have stopped the Qassams. Besides, any ceasefire will involve easing the blockade, so Israel will end up making those concessions anyway.

Second, if Israel hoped to break Hamas' hold on Gaza it has gone precisely the wrong way about it. Its leaders have done this many times before, repeatedly misreading the way Arab societies work. They believe that if they hit Gaza (or Lebanon) hard enough, the local population will blame Hamas (or Hezbollah) for bringing tragedy upon them. But it doesn't work like that. Instead, Gazans blame Israel - and close ranks with Hamas. "Anything which doesn't kill Hamas makes them stronger," says Agha, noting the way the organisation has been lionised in recent days across the Arab world, hailed as a defiant party of resistance, turning it into a "regional phenomenon".

Third, Israel's best hopes lie with the so-called moderate Arab leaders. But they have been badly undermined by this exercise, and none more so than the Palestinian president, Mahmoud Abbas, whose peace talks with Israel now look like consorting with a brutal enemy.

And this is without mentioning the fresh supply of hatred Israel has stored up against itself, creating a new generation of Gazans bent on revenge. Every child who witnessed this week's bombing is another recruit for the violence of the future.

So, yes, there may be short-term advantage for Israel's politicians, eyeing the election calendar, in hitting Hamas hard. But the senior European official who told me that this is "tactics, not strategy by the Israelis, who are expert in dealing with symptoms, not causes" is surely right. This is the act of a nation that has plenty of tactics for war - but no strategy for peace.

If it did, it would realise that Israel cannot pick the Palestinians' leaders for them, that Hamas - however repulsive its charter - is part of the Palestinian reality and will eventually have to be accommodated. Such a peace strategy would see a decision to withdraw from almost all of the West Bank and end settlement expansion, thereby making Abbas - and the peace process - credible in the eyes of his own people.

But there is no such peace strategy, only an Israeli leadership so dazzled by its own military might that it has come to believe that force is almost always the answer - and the way to avoid the toughest questions.